In recent years, the development of biodegradable plastics has been becoming active as materials for solving problems that plastic wastes cause a large burden to be imposed onto the global environment, examples of the problem including an effect onto ecological systems, the generation of harmful gases when the wastes are burned, and global warming based on a large quantity of burning calories thereof.
Carbon dioxide emitted when plant-originating biodegradable plastics out of the biodegradable plastics are burned is originally present in the air. Thus, the plant-originating biodegradable plastics do not cause an increase in carbon dioxide quantity in the atmosphere. This matter is called carbon neutrality. Importance is attached to the matter under the Kyoto Protocol, in which target values are set for carbon dioxide reduction. Thus, an active use of the plant-originating biodegradable plastics has been desired.
Recently, from the viewpoint of biodegradability and carbon neutrality, attention has been paid to polyester resins of plastics originating from plants, in particular, to polyhydroxyalkanoate (hereinafter may be referred to as PHA) resins. Furthermore, out of the PHA resins, attention is paid to the followings: poly(3-hydroxybutyrate) homopolymer resin, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer resin, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer resin, polylactic acid, and others.
However, it is known that the polyester resins are small in crystallization speed. Thus, when subjected to forming, the resins need to be cooled for a long cooling period for solidification after heated and melted, so that the resins have problems of being poor in processability and productivity.
Accordingly, in order to improve the crystallization of PHA type resins, the following has been hitherto suggested (for example, Patent Literature 1): the blend of an additive as a crystallization nucleating agent, examples of the additive including boron nitride, titanium oxide, talc, sugar alcohol, polyvinyl alcohol, chitin, and chitosan. However, under the actual circumstances, there has not yet been substantially found out, as the crystallization nucleating agent for PHA resins, any agent having a great advantageous effect. Thus, a further improvement has been desired.